Known examples of a gas sensor used for improving the fuel consumption of an internal combustion engine such as an automobile engine or for combustion control include an air-fuel-ratio sensor, and an oxygen sensor for detecting the oxygen concentration of exhaust gas.
Such a gas sensor generally has a structure in which a sensor element for detecting the concentration of a specific gas is held by a metallic shell, and electrode take-out portions (electrode pads) disposed on the surface of a rear end portion of the sensor element are surrounded by a tubular separator formed of ceramic. Terminal members attached to the separator are electrically connected to the respective electrode pads of the sensor element, a grommet (seal member) formed of rubber is disposed on the rear side of the separator, and the separator and the grommet are covered with an outer sleeve formed of metal. Lead wires are connected to the terminal members, and the lead wires are passed through through-holes of the grommet and are extended to the outside.
As a result of a rear end portion of the outer sleeve being crimped, the grommet is pressed toward the separator, whereby the separator is held between the grommet and a holding member located on the forward side of the separator.